High-precision positioning instruments are used to drive stages to desired positions in a fast and accurate manner. Typically, high-precision positioning instruments use a coarse and fine stage arrangement, wherein the fine stage is carried by the coarse stage. The coarse stage quickly moves from one position to the next, while the fine stage precisely positions the device.
Various well known mechanisms are used to drive the stages in a high-precision positioning instrument. For instance, conventional coarse and fine stages are often driven with linear servo actuators or electro-mechanical stepping motors. These mechanisms, however, have disadvantages including slow acceleration of the stages, producing an undesirable amount of heat, and being difficult to precisely control.
Another mechanism used to drive the stages in a high-precision positioning instrument is a magnetic actuator. A magnetic actuator uses an electro-magnet to move a stage from one position to another. A current transmitted through windings in the magnetic actuator generates the magnetic force used to accelerate the stage. The amount of force used to move the stage in the desired manner is controlled by generating the appropriate amount of current. Unfortunately, conventional methods of controlling magnetic actuators are imprecise because the force generated by a magnetic force falls off in a non-linear manner relative to the distance between the actuator and the object being controlled. Previous attempts to precisely control conventional magnetic actuators have resulted in a small quantity of force or a slow acceleration of the stages and the generation of excessive RMS (root mean square) power gains, which produces heat. Consequently, magnetic actuators are not typically used in conventional high-precision positioning instruments.